The present invention relates to a two-dimensional image detector, which includes connecting terminals (input/output terminals, mainly input terminals in a display device) for connecting electrode wires of an active-matrix substrate to the outside, and which is connected to the outside via an anisotropic conductive adhesive, and further concerns an active-matrix substrate and a display device. To be specific, the present invention relates to an active-matrix substrate which can be readily connected to the outside at a low temperature and maintain a resistance value at a fixed value, a two-dimensional image detector using the same, and a display device.
Conventionally, a two-dimensional image detector for radiation has been known with the following construction: semiconductor sensors, each being provided with a semiconductor layer, a pixel electrode, and others for detecting an X-ray and generating electric charge (electron-hole pair, namely, with photoconductivity), are two-dimensionally disposed in a matrix form (in column and row directions), each of the pixel electrodes is provided with a switching element, and the electrical switches are successively turned on for each raw and the electric charge is read for each column.
A specific structure and principle of such a two-dimensional image detector are described in xe2x80x9cD. L. Lee, et al., xe2x80x98A New Digital Detector for Projection Radiographyxe2x80x99, SPIE, 2432, pp. 237-249, 1995xe2x80x9d (published in 1995), xe2x80x9cL. S. Jeromin, et al., xe2x80x98Application of a-Si Active-Matrix Technology in a X-ray Detector Panelxe2x80x99, SID 97 DIGEST, pp. 91-94, 1997xe2x80x9d (first edition is published in May, 1997), and Japanese Laid-Open Patent Publication No. 342098/1994 (Tokukaihei 6-342098, published on Dec. 13, 1994).
The following explanation describes the structure and principle of a typical two-dimensional image detector for radiation.
FIG. 6 is a schematic diagram showing the construction of the two-dimensional image detector for radiation. Further, FIG. 7 is a schematic diagram showing a sectional structure for one pixel of the two-dimensional image detector for radiation.
As shown in FIGS. 6 and 8, the two-dimensional image detector for radiation is provided with an active-matrix substrate 51 having electrode wires (gate electrode group 52 consisting of a plurality of gate electrodes G1, G2, G3, . . . , and Gn and source electrode group 53 consisting of a plurality of source electrodes S1, S2, S3, . . . , and Sn) in an XY matrix form, a TFT (thin film transistor) 54 and a storage capacitor (Cs) 55, on a glass substrate. Moreover, input/output terminals are disposed on ends (not shown) of the active-matrix substrate 51. Furthermore, a photoconductive film 56, a dielectric layer 57, and an upper electrode 58 are formed on virtually the entire surface of the active-matrix substrate 51.
The storage capacitor 55 has a construction in which a Cs electrode 59 is opposed via an insulating film 61 to a pixel electrode 60 connected with a drain electrode of the thin-film transistor 54.
For the photoconductive film 56 (amorphous semiconductor layer), a semiconductive material is used to generate electric charge (electron-hole pair) by exposure to radiation such as an X-ray. According to the aforementioned literatures, amorphous selenium (a-Se) is used as a semiconductor material, which has high dark resistance and favorable photoconductivity and can form a large film by evaporation. The photoconductive film (a-Se) 56 is formed with a thickness of 300-600 xcexcm by using a vacuum evaporation method.
Further, an active-matrix substrate, which is formed in a manufacturing process of a liquid crystal display device, can be applied to the aforementioned active-matrix substrate 51. For example, the active-matrix substrate used for an active matrix liquid crystal display device (AMLCD: Active Matrix LCD) is provided with the TFT made of amorphous silicon (a-Si) or polysilicon (p-Si), an XY matrix electrode, and a storage capacitor. Therefore, only if a few changes are made in arrangement, the active-matrix substrate can be used for the two-dimensional image detector for radiation.
The following explanation describes a principle of operations of the two-dimensional image detector for radiation having the above-mentioned structure.
Electric charge (electron-hole pair) is generated in the photoconductive film 56 when the photoconductive film 56 such as an a-Se film is exposed to radiation. As shown FIGS. 6 through 8, the photoconductive film 56 and the storage capacitors (Cs) 55 are electrically connected in series with each other; thus, when voltage is applied between the upper electrode 58 and the Cs electrode 59, electric charge (electron-hole pair) generated in the photoconductive film 56 moves to a positive electrode side and a negative electrode side. As a result, the storage capacitors (Cs) 55 stores electric charge. Further, an electron blocking layer 62 made of a thin insulating layer is formed between the photoconductive film 56 and the storage capacitor (Cs) 55. The electron blocking layer 62 acts as a blocking photodiode for preventing electric charge from being injected from one side.
With the above-mentioned effect, the thin-film transistor (TFT) 54 is turned on in response to input signals of gate electrodes G1, G2, G3, . . . , and Gn so that the electric charge stored in the storage capacitors (Cs) 55 can be applied to the outside from source electrodes S1, S2, S3, . . . , and Sn. The gate electrode group 52 and the source electrode group 53, the TFT 54, the storage capacitors 55, and the like are made in a matrix form; therefore, it is possible to obtain two-dimensional image information of an X-ray by on lines sequentially scanning signals inputted to gate electrodes G1, G2, G3, . . . , and Gn.
Additionally, in the case when the used photoconductive film has photoconductivity for a visible ray and an infrared ray as well as for the radiation such as an X-ray, the above-mentioned two-dimensional image detector for radiation acts as a two-dimensional image detector for detecting the visible ray and the infrared ray. For example, the a-Se film has favorable photoconductivity to a visible ray, and an image sensor with a high sensitivity has been developed by using an avalanche effect of applying a high electric field.
Incidentally, the two-dimensional image detector for radiation is provided (packaged) with a xe2x80x9cdriving circuitxe2x80x9d (driving IC) for applying a driving voltage for the switching element (TFT) to the gate electrode group 52 and the source electrode group 53 on ends of the active-matrix substrate 51, and a xe2x80x9creading circuitxe2x80x9d (reading IC) for reading information on an image. Upon mounting (packaging) these circuits, TCP (Tape Carrier Package) method and COG (Chip on Glass) method are mainly used.
FIG. 9(a) shows an example of an arrangement of package in accordance with TCP method. In TCP method, a wire pattern is formed by copper foil and the like on a TCP substrate 67 having a base film made of a material such as polyimide, and electric members including a driving IC 65 and a reading IC 66 are mounted thereon. One end of the TCP substrate 67 is connected to input/output terminals (not shown) disposed on ends of the active-matrix substrate 51, and the other end is connected to an external circuit substrate (PWB: Printed Wiring Board) 68.
Further, FIG. 9(b) shows an example of an arrangement in accordance with COG method. In this method, the driving IC 65 and the reading ID 66 are directly mounted and connected onto the active-matrix substrate 51 (namely, glass substrate) of the two-dimensional image detector for radiation. Additionally, power and a signal is inputted and outputted to the driving IC and the reading IC 66 by using an FPC (Flexible Printed Circuit) substrate 69. Moreover, as an application of COG method, it is possible to form the driving IC 65 and the reading IC 66 in a monolithic manner upon manufacturing the active-matrix substrate 51.
In the above mounting methods, as for connection between the TCP substrate 67 and the active-matrix substrate 51 (TCP connection), connection between the active-matrix substrate 51 and the driving IC 65 or the reading IC 66 (COG connection), connection between the FPC substrate 69 and the active-matrix substrate 51 (FPC connection), and other connections, a bonding part 63 made of an anisotropic conductive adhesive is usually provided.
The anisotropic conductive adhesive used as the bonding part 63 is obtained by evenly dispersing conductive particles into a resin (binder) having adhesion. A film-type and a past-type adhesives are available. An special adhesive is also available, in which conductive materials are formed into columns in a bonding film. A thermosetting resin and a thermoplastic resin are generally adopted as the binder used for the anisotropic conductive adhesive. Table 1 shows connecting conditions of representative anisotropic conductive adhesives.
According to Table 1, when a conventional thermosetting resin and thermoplastic resin are used for the anisotropic conductive adhesive, a heating operation of (150xc2x0 C. or more)xc3x97(5-30 seconds) is normally necessary in order to obtain adhesion and conductivity by using a thermosetting reaction or a thermoplastic operation of the above resins while pressurizing.
However, regarding the two-dimensional image detector using the conventional thermosetting resin and thermoplastic resin, when the driving IC 65 and the reading IC 66 are packaged on ends of the active-matrix substrate 51 by using TCP method and COG method, heat applied from the outside to cure the anisotropic conductive adhesive is conducted via the active-matrix substrate 51 to the a-Se film (photoconductive film 56) formed on the active-matrix substrate 51, particularly to a part of the a-Se film that is located around an image pick-up area. Specifically, when heat is conducted to the a-Se film, the following problem occurs.
Generally, the a-Se film is formed by evaporation at 60-80xc2x0 C. or more so as to be amorphous with high dark resistance of about 1012 xcexa9cm; thus, the a-Se film has proper characteristics for the two-dimensional image detector. However, when a heating operation is performed after the film is formed, the dark resistance decreases to a maximum of about 105 xcexa9cm. This is because the crystallization of the amorphous a-Se film is developed by heat. Moreover, it has been known that the crystallization of the a-Se film is developed at a relatively low temperature of 60-80xc2x0 C. as well as at a high temperature.
Generally, in the two-dimensional image detector for radiation, the a-Se film is used as the photoconductive film. One of the reasons is that it is possible to obtain an image signal with excellent sensitivity to an X-ray (S/N ratio: signal to noise ratio) because of its high dark resistance. Therefore, dark resistance reduced by heat is a critical problem to the two-dimensional image detector for radiation.
In order to avoid such a problem, a method is available, in which the driving IC and the reading IC are mounted on the active-matrix substrate by using TCP method and COG method, and the a-Se film is formed at room temperature.
However, it is necessary to provide a process of putting the active-matrix substrate, on which the driving IC and the reading IC are mounted, into a vacuum chamber, and the a-Se film is evaporated. Thus, during the process, a possibility of damage increases on the driving IC and the reading IC. Further, when the a-Se film is formed by an automatic mass-producing apparatus, a special system for transporting a substrate is necessary to prevent damage on the driving IC and the reading IC.
Moreover, as the active-matrix substrate, it is possible to adopt an active-matrix substrate formed in the process of manufacturing a liquid crystal display device. The active-matrix substrate having the above construction can be effectively used as an active-matrix substrate of the liquid crystal display device and the like as well as the above two-dimensional image detector. In recent years, there has been a growing need for a larger model, high definition, and lower cost regarding a display device using the active-matrix substrate. Particularly, in order to realize high definition, upon connecting the connecting terminals (input/output terminals, mainly input terminals in a display device) to the outside so as to connect the active-matrix substrate and the outside, high connecting accuracy is required.
The objective of the present invention is to provide an active-matrix substrate, which can readily make a connection with the outside at a low temperature and maintain a resistance value at a fixed value, and to provide a two-dimensional image detector and a display device, that use the active-matrix substrate. Especially, the objective of the present invention is to provide the two-dimensional image detector which can prevent degradation in a characteristic of an amorphous semiconductor layer, that is caused by heating upon making a connection with the outside, and can maintain sensitivity to detect an image. Further, the objective of the present invention is particularly to provide the display device with high definition.
The inventor et al. has continued their studies in earnest in order to overcome the aforementioned problems. As a result, they have completed the present invention with the following findings: an anisotropic conductive adhesive, which is used for connecting the two-dimensional image detector and an external device or connecting the display device and the external device, has a photo-curing property so as to lower a heating temperature upon making a connection; electrodes including metal electrodes are used as electrode wires on an active-matrix substrate, which serves as a substrate part of the two-dimensional image detector, and at least parts of connecting terminals, which serve as bonding parts for electrically connecting the electrodes and the outside, have the property of transmitting light, so that it is possible to readily use the anisotropic conductive adhesive, which has photo-reactivity and can be connected at a low temperature, as an adhesive connecting the connecting terminals with the outside, and it is possible to prevent degradation in a characteristic of the amorphous semiconductor layer while maintaining a resistance value within a fixed range; consequently, sensitivity to detect an image can be maintained. Moreover, the inventor et al. reached the following findings: the active-matrix substrate is used for the display device, so that it is possible to readily use the anisotropic conductive adhesive, which has photo-reactivity and can be connected at a low temperature, as an adhesive for connecting the external terminals to the outside, and it is possible to prevent degradation in positioning accuracy, that is caused by thermal expansion of the substrates and the connecting members and to maintain a resistance value within a fixed range; consequently, it is possible to provide the display device with high definition.
In the present invention, the anisotropic conductive adhesive, has photo-reactivity (the photoreactive anisotropic conductive adhesive) includes an adhesive (photo-curing adhesive) in which a curing reaction is developed by irradiation of light such as an ultraviolet ray and a visible ray, and an adhesive (photo-assist thermosetting adhesive) in which activation is improved by irradiation of light such as an ultraviolet ray and a visible ray and a curing reaction is developed by a heating operation at a relatively low temperature.
In order to achieve the above objective, the two-dimensional image detector of the present invention is characterized by including (a) the active-matrix substrate which is provided with the electrode wires disposed in a lattice form, a plurality of switching elements disposed respectively at intersections of the electrode wires, and the connecting terminals for connecting the electrode wires to the outside, and (b) the amorphous semiconductor layer formed with electromagnetic wave conductivity on the active-matrix substrate, wherein the electrode wires include metal electrodes, at least parts of the connecting terminals have the property of transmitting light and are connected to the outside via the anisotropic conductive adhesive having photo-reactivity.
Further, in order to achieve the aforementioned objective, the two-dimensional image detector of the present invention is characterized by including the electrode wires disposed in a lattice form; a plurality of the switching elements disposed respectively at the intersections of the electrode wires; the amorphous semiconductor layer having electromagnetic wave conductivity; an image detecting section for detecting an electromagnetic wave image, which is emitted into the amorphous semiconductor layer, in response to a control signal inputted to the electrode wires; the connecting terminals which are connected with the outside as input/output terminals, input a control signal into the electrode wires so as to detect the electromagnetic wave image emitted into the amorphous semiconductor layer, and output an image signal according to the electromagnetic wave image; and the bonding part for electrically connecting the connecting terminals to the outside, wherein the electrode wires include metal electrodes, at least parts of the connecting terminals have the property of transmitting light, and the bonding part is made of the anisotropic conductive adhesive having photo-reactivity.
According to the above arrangement, the electrode wires include the metal electrodes, so that it is possible to maintain a resistance value within a fixed range. Additionally, with this arrangement, at least parts of the connecting terminals, which connect the electrode wires on the bonding part to the outside, have the property of transmitting light, so that it is possible to readily use the anisotropic conductive adhesive having photo-reactivity upon making a connection to the outside. Further, upon making a connection with the outside, the anisotropic conductive adhesive having photo-reactivity is used so as to lower a heating temperature of the connection. Therefore, a heating operation at a high temperature is not necessary when the bonding part is connected to the outside; thus, it is possible to prevent crystallization from developing in the amorphous semiconductor layer during the heating operation. Hence, this arrangement makes it possible to prevent degradation in a characteristic such as high dark resistance of the amorphous semiconductor layer. Therefore, according to the above arrangement, it is possible to favorably maintain sensitivity to detect an image.
Furthermore, in order to achieve the aforementioned objective, the active-matrix substrate of the present invention is characterized by including the electrode wires disposed in a lattice form, a plurality of the switching elements disposed respectively at the intersections of the electrode wires, and the connecting terminals for connecting the electrode wires to the outside, wherein the electrode wires include the metal electrodes, and at least parts of the connecting terminals have the property of transmitting light.
According to this arrangement, the electrode wires include the metal electrodes so as to maintain a resistance value within a fixed range. Additionally, with this arrangement, at least parts of the connecting terminals have the property of transmitting light, so that when the connecting terminals are connected to the outside, for example, to an external member such as an electric circuit by using the anisotropic conductive adhesive which has photo-reactivity, in TCO method or COG method, it is possible to readily use the anisotropic conductive adhesive which has photo-reactivity as an adhesive for connecting the connecting terminals to the outside, and a connection to the outside can be readily made at a low temperature.
Thus, the above active-matrix substrate is suitable for the two-dimensional image detector and the display device. The active-matrix substrate is used for the substrate parts of the two-dimensional image detector and the display device, so that it is possible to prevent degradation in a characteristic of the amorphous semiconductor layer and degradation in positioning accuracy, that is caused by thermal expansion of the substrates and the connecting members, while maintaining a resistance value at a fixed value. Consequently, the active-matrix substrate is used so as to favorably maintain sensitivity to detect an image of the two-dimensional image detector, and higher definition can be realized in the display device.
Further, in order to achieve the aforementioned objective, the display device of the present invention is characterized by including (a) the active-matrix substrate which is provided with the electrode wires disposed in a lattice form, a plurality of the switching elements disposed respectively at the intersections of the electrode wires, and the connecting terminals for connecting the electrode wires to the outside, and (b) an opposing substrate which is disposed so as to oppose the active-matrix substrate via an electro-optical medium, wherein the electrode wires include the metal electrodes, and at least parts of the connecting terminals have the property of transmitting light and are connected to the outside via the anisotropic conductive adhesive having photo-reactivity.
According to this arrangement, the electrode wires include the metal wires so as to maintain a resistance value within a fixed range. Additionally, with this arrangement, at least parts of the connecting terminals, which connect the electrode wires on the bonding part to the outside, have the property of transmitting light, so that it is possible to readily use the anisotropic conductive adhesive which has photo-reactivity upon making a connection to the outside. Further, upon making a connection to the outside, the anisotropic conductive adhesive which has photo-reactivity is used so as to lower a heating temperature of the connection. Therefore, a heating operation at a high temperature is not necessary when the bonding part is connected to the outside; thus, a heating temperature can be lowered upon connecting the input/output terminals to the outside, and it is possible to prevent degradation in positioning accuracy, that is caused by thermal expansion of the substrates and the connecting members. Therefore, it is possible to improve connecting accuracy of the display device while maintaining a resistance value within a fixed range, so that higher definition can be realized in the display device.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.